Alain Bosseboeuf

Highly decoupled single-crystal silicon resonators: an approach for the intrinsic quality factor

Special attention has been paid in this work to use all possible means to measure an intrinsic quality factor (Q) for silicon beam resonators realized on SOI wafers. Specifically, this work points to the energy dissipation into the support; a model is given and a high insulating system for clamped–clamped and clamped-free configurations has been studied, preserving the resonating element from support damping. Finite element analysis on these structures evidences values of Qsupport higher than 107. Out-of-plane and in-plane vibration Q values up to 1.0 × 105 have been measured under a high vacuum using, respectively, laser Doppler vibrometry and stroboscopic optical microscopy combined with image processing. The results have shown good agreement with thermoelastic theory. However, the observed agreement on the resonator dimension dependences is limited to quality factors lower than 3.0 × 104. Beyond these values, a physical limitation is evidenced in both cases (in-plane and out-of-plane) which does not match with the surface and clamping models listed. The role of the SOI wafers oxide layer is discussed as a possible source of dissipation.

Fabrication of a gray-tone mask and pattern transfer in thick photoresists

A low-cost gray-tone mask fabrication for thick resist UV lithography is described. The experimental relation between the theoretical transmission and the remaining resist thickness after development is presented.

Concepts and limits for the miniaturization of silicon differential vibrating inertial micro-beam accelerometer

In this paper, an original differential VBA: the ISA-100 structure including an isolating system is presented in order to explore the fundamentals parameters for the miniaturization of such devices (4 to 1 mum thick beam). The bias stability of the sensor depends directly on the frequency stability of each beam, and thus requires a high quality factor Q. Q values up to 2.4 times 105 have been measured for 3 mum thick resonators. But high Q values are an advantage up to a certain extent. Indeed as the sensitive element gets thinner and Q values get higher, resonators are more susceptible to nonlinear effects. Experiments have revealed a nonlinear behaviour for a deflection lower than 10 nanometers. The influence of the Q-factor on the nonlinear behaviour of the VBA and then on its resolution (noise level) and frequency stability is studied.

High-Q silicon flexural resonators for vibrating inertial sensors: Investigations of the limiting damping mechanisms

In designing micro-scale vibrating sensors, the achievement of very high quality factor (Q) resonators working in bending mode remains a major issue. Special attention has been paid in this work to explore the Q limitations of single-crystal silicon bending beam resonators and their dependences on geometry, temperatures and pressure for a large range of resonators. In order to preserve the resonating element from support damping, a system with high decoupling efficiency has been optimized using FEM analyses and implemented. Quality factor as a function of frequency shows the transition between thermoelastic damping (TED) and surface damping as limiting mechanism with the miniaturization of the resonators: At high vacuum, the thermoelastic theory is experimentally validated to be the main damping source for Q up to 4.0x104. Beyond these values (Q > 1.4x105) the surface effects are evidenced and characterized with thickness and frequency variations.

MEMS Process by Film Transfer Using Fluorocarbon Anti-Adhesive Layer

A low cost and low temperature microelectromechanical systems (MEMS) transfer process is presented. The process is based on adhesion control of molded electroplated Ni microstructures on the donor wafer by using a plasma deposited fluorocarbon film. Adhesive bonding of the microstructures on the target wafer using BCB sealing enables mechanical tearing off from the donor wafer. This proposed process has allowed us to realize from 7 � m down to 700 nm thick Ni patterns on Si, Pyrex glass wafers and Kapton foils. Multiple transfers lead to Ni stacked microstructures. We demonstrated the interest of a simple film transfer process for the elaboration of 3D microstructures.

An Experimental Study of Nonlinear Limits in High-Q Silicon Vibrating Micro-and Nanomechanical Sensors

In designing micro-scale vibrating sensors, the achievement of very high quality factor (Q) resonators working in bending mode remains a major issue. Nevertheless even though a high Q has several advantages, it enhances the chance of nonlinear vibrations. Special attention has been paid in this work to explore experimentally the nonlinear limitations of single-crystal silicon bending beam resonators as a function of the quality factor and the geometry of the resonator using an original ex-situ measurement technique with a detection limit down to 1 nm.

Improvement of a classical electrodeposition process for electrostatic variable-capacitance, side-drive micromotor fabrication

An improvement of a classical electrodeposition process through a photoresist mold for electrostatic side-drive micromotor fabrication is proposed. A step of selective and quasi-conformal deposition is used to reduce the air gap and bearing clearance below the value allowed by the maximum photoresist aspect ratio. This will allow the fabrication of variable-capacitance micromotors with better operation characteristics.